The Google cluster is an amazing thing. 189 teraflops and 10s of 1000s of machines.
From How many Google machines:
Assuming that the 1Ghz chip is going at about a third the gigaflops of a 2Ghz processor (3.3Gflops), we can then guess at the size of the Google supercomputer. Just for the sake of argument, let's go with 1 Gigaflop per processor. This means that the Google supercomputer has about 189 teraflops of power on the low end of my estimates, 253 teraflops on the middle end, and 316 teraflops on the high end. This would easily put it on top of the list of fastest computers in the world.
Any way you slice it, that's a lot of power.